A technique termed OpenFlow has been proposed these years, as indicated in Patent Literature 1 and in Non-Patent Literatures 1, 2. The OpenFlow grasps communication as an end-to-end flow and performs routing control, recovery from malfunctions, load balancing and optimization on the flow-by-flow basis. An OpenFlow switch, operating as a relaying device, includes a secure channel for communication with an OpenFlow controller which is comprehended as a control apparatus or controller. The OpenFlow switch is run in operation in accordance with a flow table which is optionally commanded to be amplified or rewritten from the OpenFlow controller. In the flow table, a set of matching rules (header field) to match to a packet header against, flow statistic information (Counters) and an action(s) (Action or Actions) are defined on the flow-by-flow basis. The Action or Actions define processing contents applied to a packet matched to the set of matching rules (header field) (see FIG. 12).
On receipt of a packet, the OpenFlow switch retrieves, from the flow table, such entry having matching rules matched to the header information of the received packet (see the header field of FIG. 12). If, as a result of the retrieval, the entry matched to the received packet is found, the OpenFlow switch updates the flow statistic information (Counter) at the same time as it executes the processing contents as stated in an action field of the entry for the received packet. Examples of the processing contents include packet forwarding from a specified port, packet flooding and packet dropping. If, as a result of the retrieval, no entry matched to the received packet is found, the OpenFlow switch forwards the received packet to the OpenFlow controller over a secure channel to request the OpenFlow controller to decide on a path of the packet based on the source and destination of transmission of the received packet. The OpenFlow switch receives a flow entry which will comply with the request to update the flow table. The OpenFlow switch thus forwards the packet using the entry stored in the flow table as the processing rules.
Patent Literature 2 shows a relaying device including a port move detection circuit that detects port move produced when a frame has arrived from a path learned in a MAC address table.